The present disclosure related to a method and a controller for controlling an AC generator which is used in connection with a wind turbine having a variable speed. The multi-phase generator is connected to a controllable converter and is controlled to provide a desired power or a desired torque. An AC reference signal is generated, which would provide the desired power or torque. A P+Resonant converter may be used to control an electrical characteristic of the generator in view of the reference, by applying control signals to the controllable converter. Thereby, the need to transform the electrical characteristic into a rotating frame may be eliminated which provides for a less complex controller.